Canula sealing apparatus

ABSTRACT

Cannula sealing apparatus includes a housing having a central axially facing aperture. A surgical instrument of 10.5 mm may seal with that aperture. Alternatively, a sealing member having an aperture that will seal with a 12 mm surgical instrument can be swung up to be aligned with the aperture. If a 10.5 mm instrument is required then a seal member can be swung up to have its seal aperture located over the central aperture. Each seal member is pivotal about a common axis. Each seal member has a surface that faces a housing such that both parts can seal at their facing surfaces when either of the seal members are swung up into the position where the opening is over the central opening.

TECHNICAL FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to cannula sealing apparatus and methodsof using cannula sealing apparatus. The present invention isparticularly suited to such apparatus where surgical instruments ofdifferent sizes are required to be sealed with the same cannula sealingapparatus.

U.S. Pat. No. 5,512,053 describes a surgical cannula with a slidablereducer assembly to sealingly accommodate surgical instruments. Thereducer assembly consists of multiple apertures having varying diameterssuch that the assembly can slide to selectively accommodate the exteriorof surgical instruments having a variety of outer diameters.

U.S. Pat. No. 5,843,040 discloses a surgical sleeve that includes ahousing having an opening through which surgical instruments areintroduced into the surgical sleeve. A sleeve portion extends from thehousing and has an inner diameter coaxial with the opening in thehousing. A reducer assembly is removably secured to the housing andincludes a rigid seal for rotation in a plane transverse to the sleeveportion. A resilient, laminar seal layer is generally coextensive withthe seal disc and is disposed between the disc and the housing tosealingly engage a portion of the housing. A plurality of apertures areformed in the seal disc and seal layer and have varying diameters todefine seals that are selectively movable, by rotation of the seal disc,over the opening in the housing to seal against exteriors of instrumentsdisposed in the sleeve.

U.S. Pat. No. 5,201,714 provides a cannula for laparoscopic surgerywherein the cannula comprises a housing and an elongated tube with apassageway formed within the housing so that laparoscopic instrumentsmay be passed through the housing and the elongated hollow tube into theabdominal cavity of a patient. A pair of rollers are mounted within thehousing, the rollers being spring-urged together to close the passagewaythrough the housing when an instrument is withdrawn. A slidable platehaving apertures of different sizes are mounted in the housing with theapertures provided with slitted seals therein to close the passagewaythrough the housing. The varying sized apertures in the slidable platepermit laparoscopic instruments of varying diameters to be used and tomaintain an effective seal around the instrument.

WO 94 178 444 discloses a seal for use with a surgical instrument toprovide a gas tight seal with the instrument having a diameter within awide range of diameters. The seal comprises a seal body, an instrumentseal, and a laterally compliant seal mounting. The seal body includes abore through which the instrument is passed. The instrument seal extendsradially outwards from an instrument port formed in the instrument sealthrough which the instrument is passed, and also extends axially fromthe instrument port in the direction opposite to that in which theinstrument is passed through the instrument port. The laterallycompliant seal mounting mounts the instrument seal to the seal body,forms a gas tight seal between the instrument seal and the seal body,and allows the instrument seal to move freely laterally in response tolateral movement of the instrument.

U.S. Pat. No. 5,607,397 and U.S. Pat. No. 5,569,206 disclose adaptorsthat can be attached around the cannula handle. The adaptors include asmaller seal that projects to one side of the handle and which can bepivoted over the handle about an axis perpendicular to the elongate axisof the cannula and to one side of that axis.

SUMMARY OF THE INVENTION

It is an object of the present invention to attempt to overcome at leastone of the problems associated with the above publications or otherproblems.

The present invention is defined in the claims appended hereto andelsewhere in the specification.

The opening in the housing may comprise a seal member.

The seal members may be provided on a first part of the apparatus thatis detachable from a second part of the apparatus. A valve may bearranged to inhibit a flow of gas in at least one direction when nosurgical instrument is being sealed by a seal member. At least one sealmember may be arranged to be movable by the instrument of a surgeon.

The resilient seal or seals may include a circular hole for sealingagainst the instruments.

The pivotable member may include a resilient seal.

According to one embodiment of the invention, engagement of the frictionmember when the pivotable member moves between the positions, causes thefriction member to deform.

According to another embodiment of the invention, when the pivotablemember moves from the inoperative position to the operative position,during at least part of that movement, the friction member has noeffect.

According to yet another embodiment of the invention, the pivotablemember includes a channel spaced from a recess whereby, when moving thepivotable member from the inoperative to the operative position therelative movement causes the pivotable member to first be located in thechannel, then frictionally engaging the space between the channel andthe recess and then to engage with the recess.

According to yet another embodiment of the invention, the frictionmember locates in the recess when the pivotable seal is in the useableposition.

According to yet another embodiment of the invention, the channelcomprises an end section that is ramped so as to initiate deformation ofthe friction member.

According to yet another embodiment of the invention, the frictionmember comprises at least one resilient nipple.

According to yet another embodiment of the invention, at least one sealis resilient.

According to yet another embodiment of the invention, at least oneresilient seal includes the friction members.

According to yet another embodiment of the invention, the resilient sealincludes a circular opening that is supported by an adjacentnon-resilient circular support of greater diameter than that of theresilient seal.

According to yet another embodiment of the invention, the circularposition is raised.

According to yet another embodiment of the invention, the resilient sealis biased towards the circular support.

According to yet another embodiment of the invention, the distancebetween the opening of two resilient seals and the opening of theirsupports is the same.

According to yet another embodiment of the invention, the part that theseal is mounted on includes at least one clip and the removable sealincludes at least one corresponding opening that is expandable over theclip, to retain the removable seal on the housing.

According to yet another embodiment of the invention, the housingincludes a resilient seal.

According to yet another embodiment of the invention, seal members areused in a cannula instrument.

According to another embodiment of the invention, the cannula sealingapparatus includes a plurality of seal members each having a differentsized aperture with which, in use, surgical instruments of differentsizes may be inserted in a first direction to seal with a selected sealmember. At least one seal member is pivotable from an operative positionin which a surgical instrument may, in use, be inserted in the firstdirection to seal with that member and an inoperative position. Thepivot axis of the pivotal movement of the sealing member is in a seconddirection, transverse to the first direction wherein the pivotal axis ofthe seal member is arranged, in use, to pass through an insertedsurgical instrument.

According to another embodiment of the present invention, a housing ofthe apparatus includes an opening through which, in use, a surgicalinstrument may be inserted in the first direction with the seal affectedby the seal members being arranged to be in the region of that opening.The pivotal axis of the seal member is spaced from the opening in thehousing in a direction extending in the first direction.

According to yet another embodiment of the present invention, at leastone seal is resilient and includes a circular opening that is supportedby an adjacent non-resilient circular support of greater diameter thanthat of the resilient seal. The resilient seal is biased towards thecircular support.

According to yet another embodiment of the invention, when eachpivotable seal member is in the operable position, said pivotable sealmember is restricted by a friction member. The frictional memberrestricts movement of the seal member away from the operable position.

A method of using a cannula sealing apparatus according to the presentinvention comprises the steps of providing a plurality of seal memberseach having a different sized aperture with which, in use, a surgicalinstrument of a different size can be inserted in a first direction toseal with a selected seal member. At least one seal member is pivotedfrom an operative position in which, a surgical instrument may, in use,be inserted in the first direction to an inoperative position. The sealmember is pivoted about an axis extending in a second direction,transverse to the first direction to move between the operative andinoperative positions.

According to another embodiment of the present invention, a secondsurgical instrument of a different size to the first instrument is movedin the first direction to seal with the seal member of a different size.The seal member is pivoted about an axis extending in a second directiontransverse to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be carried into practice in various ways butone embodiment will now be described with reference to the accompanyingdrawings, in which:—

FIGS. 1, 2 and 3 are perspective views of a cannula sealing apparatus 10arranged to receive instruments of different sizes;

FIG. 4 is a sectional view through the apparatus, and

FIG. 5 is an exploded view of FIG. 1.

FIG. 6 is a perspective view of the cannula being operated by theinstrument.

FIGS. 7 a and 7 b are cross-sectional views of a cannula sealingapparatus 10 according to a second embodiment showing the pivot membersin different positions.

FIG. 8 is a perspective view of a housing 28.

FIG. 9 is a top view of a seal for use with the housing shown in FIG. 8.

FIG. 10 is a perspective view of a pivot member for use with the housingshown in FIG. 8.

FIG. 11 is a rear perspective view of a pivot member for use with thehousing shown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE

A reusable cannula 14 has an upwardly facing opening 16 in which a valve18 is located with an outwardly projecting lip 20 on the valve sittingon an upwardly facing annular rim 22. A gas input/output line 24 isconnected to the cannula just below the valve 18 and an on/off valve 26is provided on the line 24.

A single use seal housing 28 is detachably connected to the reusablecannula 14 with a bayonet connection comprising circumferentially spacedprojections (not shown) 30 on the housing 28 cooperating with outwardlyfacing circumferentially spaced recesses 31 on the cannula such that thehousing 28 can first be pushed down on the cannula 14 with theprojections moving along axially extending recesses and then with thehousing 28 being rotated relative to the cannula 14. The projectionsthen move along circumferentially extending recesses until end stops arereached. This locks the housing 28 on the cannula 14. This also trapsand seals the lip 20 on the rim 22 with an axially facing annularsurface 33 of the housing 28 compressing the resilient lip slightly.

The housing 28 includes a central axially facing aperture 32. Twoarcuate seal members 34 and 36 are pivotally mounted on the housing 28by pivot members 38 at each side. End stops 35 limit pivotal movement inone direction. The pivot members 38 extend perpendicularly to the axisof the cannula 14 and radially to that axis and, from the outsidetowards the axis they extend first through an arm 42 of the seal member36 and then through an arm 40 of the seal member 34 and then through thehousing 28.

In use, the housing 28 is connected to the cannula 14. A tip 44 oftrocar instrument (only the bottom part of which is shown) in FIG. 5 ispushed first through the opening 32 in a first direction then throughthe valve 18 and then along and through an elongate tube 46 of theinstrument to the position shown in FIG. 5. The instrument is theninserted through an opening 32 in the abdominal wall with the trocarinstrument expanding that opening 32 and with the exterior of the tube46 sealing with the abdominal wall opening 32. The periphery of thetrocar seals with a sealing element 37 mounted in the opening 32 of thehousing 28. Alternatively the trocar can be inserted through the opening32 when the tube 46 already extends through the abdominal wall.

The on/off valve 26 is opened and gas is supplied through the inlet.This gas flows between the trocar on the tube 46 to inflate theabdominal cavity. Endoscopic operations with any endoscopic instrumentincluding a camera instrument can then be carried out in a well knownmanner.

When the trocar is withdrawn back through the opening 32 the valve 18effects a seal such that gas from the abdominal cavity is unable toescape.

The opening 32 also comprises a seal member 37 in addition to thepivoting seal members 34 and 36. Each seal member includes a membrane(not shown) that extends inwardly and that is resilient such that thetrocar is able to seal with that opening 32. Whilst the description sofar has been in relation to trocar instruments it will be appreciatedthat any instrument used in endoscopic surgery may be used with thecannula sealing apparatus.

The diameter of the opening 32 is such that instruments of nominal 12 mmdiameter can seal with that opening 32 as shown in FIG. 2. In someinstances though instruments of different diameter may be required toseal with an opening 32 in the region of the opening 32.

When a nominal 5 mm diameter instrument is to be used the seal member 34is moved upwardly about the pivot members 38 until the centre of thenominal 5 mm diameter aperture 48 is coincident with the elongate axisof the tube 46 as shown in FIG. 1. A nominal 5 mm instrument can then beused with that instrument sealing with the seal member 34. Similarly anominal 10 mm diameter instrument can seal with the seal member 36 bypivoting the member 34 back to the position shown in FIG. 2 and movingthe seal member 36 up over the opening 32 as shown in FIG. 3. Themovement of each seal member may be initiated either by hand or by theend of the surgeon's instrument. In the latter case, as shown in FIG. 6,the tip 45 of the instrument abuts a side face of the respective sealmember 34 and relative movement between the instrument and housing 28affects the rotation of the seal member 34, 36.

The selection of a tailored seal for each trocar diameter means the feelto the surgeon pushing the instrument in or withdrawing the instrumentfrom a seal member 34, 36 is the same, regardless of the diameter ofthat member.

The facing surfaces of the housing 28 and the seal members 34 and 36must seal when the openings of the members are concentric with theopenings 32 of the housing.

To this end, whilst the arms 40 and 42 are at different axial extentsrelative to the axis of pivotal movement, the arcuate surfaces of theseal members 34, 36 that can face the opening 32, have the same partcylindrical or part spherical surface as a part cylindrical or partspherical surface of the housing 28 in the region shown by the line 50.A soft sealing surface that may be slightly resilient is applied to thesurfaces of the seal members that seal with the housing 28. This gives aconstant feel to the switching of one opening member or another.

Whilst two pivoting seal members have been described there may be moreor less than two seal members 34, 36 with, for instance, when there arethree pivotable seal members each of which may be located over the fixedcentral aperture 32, two of those members may be located to a commonside of that aperture 32. At that side, when the member furthest fromthe aperture 32 is required to be used, the one nearest to the aperture32 may first be moved over and past that aperture 32 with movement ofthe previously furthest member then being moved over the centralaperture 32.

Whilst apertures of nominal 5, 10 and 12 mm diameter have been describedit will be appreciated that apertures of any diameter may be providedsuch as 5, 7, 10, 12 and 16 mm. The larger diameter openings 32 areparticularly suited to operations effected on obese patients.Furthermore the seals maybe colour coded, so that the surgeon may easilyselect the correct seal size by visual reference to the colour.

FIGS. 7 to 10 show a second embodiment of a cannula 14. The cannula 14is substantially in accordance with the first embodiment hereindescribed wherein a single use housing 28 is detachably connected to areusable cannula 14. However, rather than the arcuate seal members 34,36 being pivotally mounted to the housing, the seal members 34, 36 aremounted to rockers 54, 56. A part cylindrical surface 50 of the housing28 includes resilient nipples 60 that engage the rockers 54, 56 toprovide a frictional resistance against movement of the rockers 54, 56towards or away from an operable position in which the arcuate sealmembers 34, 36 are concentric with the axis of the cannula 14. Forinstance, during use, rocker 54 can be freely pivoted to the positionshown in FIG. 7 a in which the nipple 60 begins to engage the rocker 54.In order to rotate the rocker 54 further towards the concentricposition, the nipple 60 must deform. The deformed nipple 60 presses onthe underside of the rocker 54 creating friction resisting movement ofthe rocker 54. When the rocker 54 reaches a concentric position, asshown in FIG. 7 b, the nipple 60 is aligned with a circular recess 90 inthe rocker 54 which allows the nipple 60 to return to its originalshape. In order to misalign the rocker 54 from this position, it isnecessary to deform the nipple 60. It has been found that thisarrangement provides sufficient friction resistance against the movementof the rockers 54 away from the operable position, such that the cannula14 will move within the patient before the rocker 14 moves in relationto the housing 28.

FIG. 8 shows the cannula housing 28 in more detail. A semi-annularprotrusion 62 extends from either side of the housing 28. A centralaxially facing aperture 32 is defined in the housing 28 by a tubularsection having an outside wall 64. Two clips 66, 68 are formed on thetop of the housing 28. The clips 66, 68 create overhanging ledges 69.The semi-annular protrusion 62, tubular section, and clips 66, 68 areformed integrally to the housing 28.

FIG. 9 shows a seal 37 that clips onto the housing 28. This seal 27 ismade from a resilient material. The seal 37 includes a central hole 70and two openings 71, 72 located on either side of the central hole 70.The openings 71, 72 correspond to the clips 66, 68 of the housing 28.Accordingly, the seal 37 can be assembled on to the housing 28 bystretching the openings 71, 72 over the clips 66, 68 and locating anarea of the seal adjacent to the flat edge 73, 74 of the openings 71, 72under the ledges 69. The seal 27 is sized so as to be stretched oralternatively or additionally slightly compressed when fitted under theledges 69. This ensures that the seal 37 is held firmly to the housing28 thereby creating a seal. The central hole 70 is also sized so as tofit tightly about the outside wall 64 of the tubular section 64. Thecentral hole 70 comprises a stepped bore wherein a thin section of theseal 37 extends over the top of the tubular section and restricts theaperture 32. When assembled to the housing 28 the edge of the centralhole 70 thereby creates a lip seal against suitably sized surgicalinstruments that are inserted through the housing 28.

The seal 37 prevents fluid from escaping the housing 28 through thecentral axially facing aperture 32 by forming a seal against the top ofthe tubular section, the outside wall 64 and the top of the housing 28.This creates a large surface area against which to seal. Furthermore thetop of the tubular section acts as a support for the seal 37 and theseal 37 may be resiliently biased against the top of the tubularsection.

When assembled to the housing 28 the seal 37 creates an outer profilesubstantially as herein described wherein the top of the housing 28presented to the rockers 54 forms a part cylindrical surface. The seal37 also includes nipples 60. Although four nipples 60 are shown, thefunction provided by the nipples 60 can be equally achieved with one ortwo nipples 60 or a plurality of nipples 60 in various arrangements. Thepart cylindrical profile is also interrupted by an annular ridge 76 thatis formed around the central hole 70. The ridge 76 is raised from thetop of the seal 37.

FIG. 10 shows the rocker 54. The rocker 56 is similar. The top of therocker 54 is arranged to accept a seal 34, 36, wherein the seal 34, 36is similar to seal 37 as described above. The rocker 54, 56 includes acentral hole 78 and two clips 79, 80 on either side of the hole. Againthe seal (not shown) is assembled to the rocker 54, 56 by stretching theopenings 71, 72 over the clips 79 and locating an area of the seal 34,36 under the ledges there formed. Again the seal 34, 36 extends over atubular section defining a central hole with the same features as thatof the seal for the housing 28.

Each rocker 54, 56 includes arms 82, 84. The arms include circularapertures 83, 85, which are sized to fit about the semi-annularprotrusions 62 on the housing 28. Stop members 86, 87 project inwardly.When assembled to the housing 28 the stop members 86 abut the ends ofthe semi-annular protrusion 62 to restrict the movement of the rocker54,56. The rockers 54, 56 are sized differently so that the arms of onerocker may fit inside the arms of the other rocker, when both areassembled to the housing 28.

FIG. 11 shows the underside of the rocker 54. The rocker 58 is similar.The circular recess 90 is formed so that, when the rocker 54 is in theconcentric position, the circular recess 90 and corresponding nipple 60is aligned. A guide channel 91 is formed extending from a leading edge92 of the rocker 54. The guide channel 91 comprises a first section thatis sized so as to accommodate the nipple 60, without deforming thenipple 60. A second section of the channel is ramped so as to initiatethe compressing of the nipple 60. The end of the second section isspaced from the circular protrusion.

When the rocker 54 is assembled to the housing 28, the rocker 54 canpivot between the inoperable and operable positions by rotating aboutthe semi-annular recesses. As mentioned, the movement is limited byabutment of the stop member. The rockers 54 and 56 may be moved betweenthe inoperable position and the operable, concentric position, byrotating the rockers 54, 56. By way of example, rocker 54 may be rotatedmanually towards the concentric position. As the leading edge 92 movesover the annular ridge 76, it compresses the ridge thereby forming aseal between the ridge and underside of the rocker 54. When the leadingedge reaches the nipple 60, the channel 91 first accommodates the nipple60 in the first section, without deforming the nipple 60. As the rocker54 is moved further, the nipple 60 engages the ramped section of thechannel 91 and the nipple 60 is urged to compress. Maximum friction iscreated as the compressed nipple 60 moves between the channel 91 andcircular recess 90. When aligned with the circular recess, the nipple 60locates therein. This acts to provide a ‘click’ functionality to therocker 54 such that the rocker 54 ‘clicks’ into the concentric position.The rocker 54 can be moved back to the stored position in a reverse ofthe above process.

Each of the three seals provided by the housing 28 or the rockers 54, 56when in place, is effected by a seal whose inner opening for theinstrument is very close to the inner edge of the tubular member thatthe seal 37 is biased towards. This ensures good support for each seal37. The radial distance from the opening of the seal 37 to the inneredge of the supporting tubular housing 28 may be substantially the samefor all three seals.

The frictional resistance provided by each seal 37 may be the same.

Either rocker 54, 56 may be moved manually or by an instrument of thesurgeon that may subsequently extend through the cannula 14. Whilst tworockers 54, 56 have been described only one may be present.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A cannula sealing apparatus including a plurality of seal memberseach having a different sized aperture with which, in use, surgicalinstruments of different sizes may be inserted in a first direction toseal with a selected seal member, at least one seal member beingpivotable from an operative position in which a surgical instrument may,in use, be inserted in the first direction to seal with that member andan inoperative position characterised in that the pivot axis of thepivotal movement of the sealing member is in a second direction,transverse to the first direction.
 2. A cannula sealing apparatus asclaimed in claim 1 in which the second direction is perpendicular to thefirst direction.
 3. A cannula sealing apparatus as claimed in claim 1 inwhich the pivotal axis of the seal member is arranged, in use, to passthrough an inserted surgical instrument.
 4. A cannula sealing apparatusas claimed in claim 1 in which at least one seal member includes spacedpivotal mountings on each side of the apparatus.
 5. A cannula sealingapparatus as claimed in claim 1 including an opening in a housing of theapparatus through which, in use, a surgical instrument is arranged to beinserted in the first direction with the seal effected by the sealmembers being arranged to be in the region of that opening.
 6. A cannulasealing apparatus as claimed in claim 5 in which pivotal axis of theseal member is spaced from the opening in the housing in a directionextending in the first direction.
 7. A cannula sealing apparatus asclaimed in claim 5 in which the pivotally movable seal member includes asurface that is arranged, in use, to surround and seal with the surfaceof the housing that surrounds the opening.
 8. A cannula sealingapparatus as claimed in claim 7 in which the surfaces of the seal memberand housing are part cylindrical.
 9. A cannula sealing apparatus asclaimed in claim 7 in which the surfaces of the seal member and thehousing are part spherical.
 10. A cannula sealing apparatus as claimedin claim 7 in which at least one surface includes a resilient material.11. A cannula sealing apparatus as claimed in claim 1 including at leasttwo pivotally movable seal members.
 12. A cannula sealing apparatus asclaimed in claim 11 in which, when both of the pivotally movable sealmembers are in the inoperative position, the seal of each seal member islocated to a different side of the first direction.
 13. A cannulasealing apparatus as claimed in claim 11 in which each seal member ispivotally movable about the same pivot axis.
 14. A cannula sealingapparatus as claimed in claim 13 in which, in the region of the pivotaxis, one seal member is axially inwards of the other seal member. 15.The cannula sealing apparatus as claimed in claim 1 wherein, when eachpivotable seal member is in the operable position, said pivotable sealmember is restricted by a friction member such that the frictionalmember restricts movement of the seal member away from the operableposition.
 16. The cannula sealing apparatus as claimed in claim 15,wherein the friction member is located on the housing.
 17. The cannulasealing apparatus as claimed in claim 15 wherein the friction memberengages with the pivotable members.
 18. The cannula sealing apparatus asclaimed in claim 15 wherein the friction member is resilient.
 19. Amethod of using a cannula sealing apparatus comprising a plurality ofseal members each having a different sized aperture comprising insertinga surgical instrument of first size in a first direction to seal with aseal member of a first size aperture and then removing that instrumentand subsequently pivoting at least one seal member from an inoperativeposition to an operative position in which a second surgical instrumentof a different size to the first instrument is moved in the firstdirection to seal with the seal member of a different size characterisedin that the seal member of a different size is pivoted about an axisthat passes through the surgical instrument when inserted.
 20. A methodof using a cannula comprising inserting a surgical instrument throughthe cannula along a first axis, and, before inserting the surgicalinstrument, selecting an appropriately sized seal member so that theselected seal member seals against the instrument, the method comprisingselecting at least one pivotable seal member and pivoting said sealmember about an axis transverse to the first axis and from an inoperableposition to an operable position, in which the seal member is coincidentwith the first axis, the method including causing a frictional member toengage the seal member, when the seal member is in the operableposition, such that the frictional member restricts the seal member frommoving away from the operable position.